There is no substitute for cubic inch or in this case surface area

In my experience there is only moderate correlation between speaker or driver size and the size of the soundstage the speaker throws. There are small bookshelf speakers with two drivers that when placed on stands and positioned properly produce a huge soundstage.

However, I must admit that the largest soundstages I have heard are from giant speakers with multiple drivers. Von Schweikert Ultra 11's, big Wilsons, and a couple other huge speakers. Another speaker that generates a huge soundstage is the MBL 101 E.

I'm running Thiel CS6 speakers and they throw a respectably large soundstage with a small number of drivers.

With smaller driver it has to move a lot to produce the same sound pressure vs. bigger drivers.  

When the small drivers move violently, it creates distortion.  

@andy2 

My Rockport Avior ii speakers can go to 25 hz. I play all types of music and even on the lowest electronic music the drivers don’t move much. I have seen smaller woofers move like you say and it’s not desirable. 

Rockport Avior ii

I wish I have your speakers.

Advancements in woofer and cabinet technology no longer require large diaphragm elements to produce accurate bass response capable of properly loading a room and producing the benefit of enhancing soundstage you seek.  The effect on soundstage is related to the accuracy of the low and mid bass, and the woofer’s ability to move enough air in correlation to room size to create  the effect.   For example, my speakers are known for the fast, articulate, and dynamic bass response with two vent loaded 5.5” woofers.  These woofers are a rigid, long throw diaphragm design that move large volumes of air even though they are small diameter drivers.  25Hz test tones are audible (a little over 3db down); however, there is a steep roll off after that and 20Hz test tones are not audible to my old ears.  This level of response is amazing from such small drivers.  In fact, multiple smaller woofer speaker designs have the advantage of wider dispersion and less beaming than older large diaphragm woofers, enhancing the soundstage better. Therefore, it is not necessary to have a large diaphragm woofer to get deep, accurate response that enhances soundstage.  

The technological advances include, but are not limited to:

1. New magnetic materials with higher field strength (higher Tesla rating). 
2. New magnetic designs (for example, my speakers use a ring magnet structure) that are more accurate and more efficient transducers of electrical to mechanical energy.
3. Long throw armature designs moving as much air as a larger diaphragm, short throw design. 
4. More rigid diagram materials and computer assisted design with less break-up effects resulting in lower distortion. 

These advances permit the design of small size woofers that have the advantages of lower distortion, speed, dispersion and accuracy while moving significant quantities of air compared to older large diaphragm designs.  Within a given brand, woofer size increases with larger, more expensive models that are usually designed for more voluminous rooms in order to correlate the volume of air moved by the speaker with room volume.